There are many examples in the prior art of miniaturized X-ray sources for medical purposes, in particular for in vivo treatment of various lesions, such as tumors, stenoses etc. They all have the problem in common of achieving as high an output power as possible in order to enable delivering a high enough and controlled radiation dose at the point of treatment. Often times the materials of manufacturing sets certain limits in this respect, since the active parts, the anode and the cathode, must be enclosed in a vacuum cavity, and the enclosure materials often absorb a good deal of the generated radiation, thereby decreasing the efficiency of the device.
It is known in the prior art to manufacture miniaturized X-ray cathodes in the form of structures having small diamond tips as X-ray emitting elements. An example of such a manufacturing method is disclosed in applicant's own U.S. provisional application Ser. No. 60/137,478 (corresponding to EP-00850097.7), the entire contents of which is incorporated herein by reference
This known method comprises providing structured silicon substrates in which e.g. pyramidal pits or depressions are etched. Then boron doped diamond is deposited on the substrate on the side having the depressions, so as to form diamond tips having a pyramidal shape, buried in the silicon substrate. Sacrificial etching (e.g. using HF:HNO33:7) of the silicon from the side opposite the side where diamond was deposited, to a desired depth exposed the diamond pyramids.
In order to control the thickness of the silicon that remains after the sacrificial etching, the etching time and etching solution composition must be carefully controlled. Certain irregularities, both in surface structure and thickness can occur, which could render the finished cathode structures difficult to assemble, in particular by bonding techniques, with other components to form a complete X-ray source.